from turtle import *
from random import *
from math import *

def tree(n,l):
    pd()            # 下笔
    # 阴影效果
    t = cos(radians(heading()+45)) / 8 + 0.25
    pencolor(t,t,t)
    pensize(n / 3)
    forward(l)       # 画树枝

    if n > 0:
        b = random() * 15 + 10 # 右分支偏转角度
        c = random() * 15 + 10 # 左分支偏转角度
        d = l * (random() * 0.25 + 0.7) # 下一个分支的长度
        # 右转一定的角度，画右分支
        right(b)
        tree(n - 1,d)
        # 左转一定的角度，画左分支
        left(b+c)
        tree(n -1,d)
        # 转回来
        right(c)

    else:
        # 画叶子
        right(90)
        n = cos(radians(heading() - 45)) / 4 + 0.5
        pencolor(n,n * 0.8,n * 0.8)
        circle(3)
        left(90)
        # 添加0.3倍的飘落的叶子
        if random()>0.7:
            pu()
            # 飘落
            t = heading()
            an = -40 + random() * 40
            setheading(an)
            dis = int(800 * random() * 0.5 + 400 * random() * 0.3 + 200 * random() * 0.2)
            forward(dis)
            setheading(t)
            # 画叶子
            pd()
            right(90)
            n = cos(radians(heading() - 45)) / 4 + 0.5
            pencolor(n * 0.5 + 0.5,0.4 + n * 0.4,0.4 + n * 0.4)
            circle(2)
            left(90)
            pu()
            # 返回
            t = heading()
            setheading(an)
            backward(dis)
            setheading(t)
    pu()
    backward(l)      # 退回

bgcolor(0.5,0.5,0.5) # 背景色
ht()                 # 隐藏turtle
speed(0)             # 速度 1 - 10 渐进，0 最快
tracer(0,0)
pu()                 # 抬笔
backward(100)
left(90)             # 左转 90 °
pu()                 # 抬笔
backward(300)        # 后退300
tree(12,100)    # 递归七层
done() 